Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $32.30   6.239%   $34.3152   $34.32   $34.30   $34.30  
  Purchase #2 $62.29   10.528%   $68.8479   $68.85   $68.85   $68.80  
  Purchase #3 $234.28   11.743%   $261.7915   $261.79   $261.80   $261.80  
  Purchase #4 $185.76   6.488%   $197.8121   $197.81   $197.80   $197.80  
  Purchase #5 $68.64   9.116%   $74.8972   $74.90   $74.90   $74.90  
  Purchase #6 $165.53   11.196%   $184.0627   $184.06   $184.05   $184.10  
  Purchase #7 $214.55   11.409%   $239.028   $239.03   $239.05   $239.00  
  7 purchase totals = $963.35       $1,060.7546   $1,060.76   $1,060.75   $1,060.70